Method for the preparation of a compression ignition engine fuel

ABSTRACT

Method for the preparation of a compression ignition engine fuel, comprising the steps of providing a mixture of a primary hydrocarbon fuel comprising one or more alcohols; and dehydrating in the mixture the one or more alcohol to its or their corresponding ether and water, to obtain the compression ignition fuel.

The present invention relates to compression ignition fuel compositions. In particular the invention concerns a method for the preparation of a compression ignition engine fuel from an alcohol containing primary fuel or by addition of an alcohol to an hydrocarbon fuel.

Today, a sustainable and common use of bio-fuel is possible with second generation alcohol containing bio-fuels. However, bio-fuels as prepared have in raw form a lower grade and do not burn in traditional compression-ignition engines.

In particular, high water content of up to 5 or 10% and a low cetane number of bio-ethanol limit its use for transportation. At the same time, stringent emissions regulations make traditional diesel fuel improper for operation without additional exhaust gas cleaning systems.

These limitations can be overcome by the use of certain additives increasing the cetane number of bio-ethanol or improving traditional fossil diesel fuels for cleaner operation. Oxygenates, for instance ethers, are known to increase the cetane number and burn without soot emissions.

The number of useful compression ignition engine fuel compositions is further reduced by practical consideration. The fuel flashpoint must be above 52° C. for storage safety reason. The amount of additive to be mixed with the fuel is also preferred to be low, typically between 1 and 5 wt % depending on the price of the additive in order to limit the cost and allow operation in a diesel engine without major engine modification.

The present invention is based on low cost and easily available additives enabling upgrade of most of the known diesel and non-diesel hydrocarbon fuel for clean use in compression-ignition engines.

In particular the fuel additive for use in preparation of a compression ignition engine fuel according to the present invention is based on solely alcohols that are cheap, widely available and safe transportation fuels on there own, but have a low cetane number when not treated further.

Accordingly this invention provides in general a method for the preparation of a compression ignition engine fuel, comprising the steps of

providing a mixture of a primary hydrocarbon fuel with one or more alcohols; and

dehydrating in the mixture at least part of the one or more alcohol to its or their corresponding ether and water, to obtain the compression ignition engine fuel.

The term “primary fuel” as used herein before and in the following description shall mean a fuel which is fuelled into a vehicle tank or into a tank for a stationary compression ignition engine and which fuel is subjected to a subsequent conversion treatment prior to be injected into the engine.

As already mentioned hereinbefore, addition of alcohol to fuel is seen to reduce the cetane number of the fuel, hence make it less suitable for compression ignition applications.

The present invention requires that the alcohol/primary fuel mixture is passed through an alcohol dehydration catalyst to ensure that a sufficient fraction of the alcohol is converted to the corresponding ether and water according to the following reaction:

R1-OH+R2-OH->R1-O-R2+H₂O

where R1 and R2 are molecules containing H, C and optionally O.

The above reaction is equilibrium limited and the resulting compression ignition fuel is a blend of hydrocarbon, alcohol, ether and water.

The primary hydrocarbon fuel comprises preferably C5-C28 hydrocarbons and/or bio-fuel.

In a specific embodiment of the invention, the primary hydrocarbon fuel comprises gasoline.

Alcohols being useful in the primary fuel are C₁ to C₁₀ monoalcohols and/or polyols.

Preferably the one or more alcohols contained in the primary fuel mixture are dehydrated in presence of a dehydration catalyst.

Suitable dehydration catalysts for use in the invention comprise all solid acids, such as alumina, silica alumina, a zeolite, tungstated oxides, sulphated oxides, alumina phosphates, materials containing sulfonic acid functional groups, such as sulfonated polystyrene, sulfonated fluorocarbon polymers, sulfonic acid functionalized oxide materials (alumina, SBA-15, silica) and mixtures thereof.

In a specific embodiment of the invention, the dehydration catalyst is arranged within a reactor on board of a vehicle.

If the primary fuel has already a suitable cetane number, addition of alcohol and catalytic dehydration enables to reduce the particles emission. The weight fraction of the alcohol to be added is adjusted depending on the desired reduction.

Example 1 illustrates this feature using ethanol to improve bio diesel and fossil diesel combustion.

Alternatively, if the primary fuel has an insufficient cetane number, addition of alcohol and catalytic dehydration to significant levels enables the thus prepared compression ignition fuel to operate a compression/ignition engine. The amount of alcohol necessary depends on the nature of the primary fuel.

Example 2 illustrates use of ethanol or butanol as diesel improver for hydrous ethanol, butanol or traditional gasoline.

EXAMPLES Example 1 Alcohol as Clean Improver for Diesel-Like Fuels

Two primary Diesel fuels, namely standard Diesel and rapseed oil (bio-Diesel) blended with ethanol were tested after upgrade according to the invention, i.e. dehydration treatment. In this example the two primary fuels can power a traditional Diesel engine without additives. Table 1 presents the fuel mixtures considered in this example with pure fossil Diesel as a reference. Three other fuel mixtures include ethanol as additive to the primary fuel. Therefore we use an on-board catalytic converter to perform the dehydration prior to injection in the engine. The conversion rate of the dehydration reaction is chosen to be 80% so that the ethanol is partly upgraded into diethyl ether (DEE) and water. This step ensures that even the mixture with high originally high alcohol content has Diesel-like properties. As shown in Table 1 that the dehydrated fuels contain amounts of alcohol as well as water in addition to DEE and the primary fuel.

TABLE 1 Fuel compositions - before and after dehydration Fuels Diesel D70E30 D50E50 Bio25E75 Composition (weight %) before up-grade Ethanol — 30 50 75 Water — — — — Rapseed oil — — — 25 Diesel 100 70 50 — Composition (weight %) after dehydration Ethanol —  6 10 15 DEE^(§) — 19 32 48 Water —  5  8 12 n-Butanol — — — — DBE^(§§) — — — — Rapseed oil — — — 25 Diesel 100 70 50 — Conversion alcohol to 80 80 80 ether % ^(§)Diethyl ether ^(§§)Dibutyl ether

For test purpose, the upgraded fuels were prepared by mixing pure components, although they could have been prepared by contacting the primary fuels with a suitable dehydration catalyst. The thus prepared compression ignition fuels were used to operate a commercial Diesel engine R4 Peugeot 1.6 liter common rail engine (DV6TED4-9 HZ) at 80 kW @4000 rpm. As the fuels differ from traditional Diesel fuel (lower heating value per volume), the engines settings were adapted for each case. For instance the fuel injection time was extended and started earlier in order to keep the pressure maximum in the range 8-12 degrees ATDC (standard Diesel operation). For each fuel test, the engine load was fitted on the reference Diesel fuel operation.

Table 2 summarizes the efficiency at a load point of 55 Nm with the fuels mentioned above after dehydration treatment.

All fuels, conventional Diesel fuel as well as the upgraded fuels, provide an efficiency of around 33-35% which is well in line with traditional Diesel operation. D50E50 shows a higher efficiency than the other mixtures and than conventional Diesel fuel. This increase causes a slight increase of CO and HC in the exhaust gas with comparable NOx emissions.

In general addition of alcohol and subsequent dehydration does not affect the exhaust gas emissions significantly but enables the engine to run with a bio- or partly bio-fuel. In addition a decrease of the particle emissions is seen when adding ethanol to the conventional Diesel fuel.

A mixture with 50 w % of ethanol showed reduced the particle emissions while keeping the Diesel-fuel properties of the mixture. When increasing the ethanol content further, the reduction is considerable (one order of magnitude), as exemplified by adding 75 w % ethanol to some traditional bio-Diesel.

It clearly shows that alcohol addition and dehydration preserves the Diesel quality of the fuel and secures Diesel engine improved efficiency and much reduced the particle emissions.

TABLE 2 Operation in a Diesel engine with load at 55 Nm Fuel Diesel D70E30 D50E50 Bio-E75 Efficiency % 34.74 36.39 41.14  33.15  NOx [g/kWh] 10.17 10.08 7.74 8.86 HC [g/kWh] 0.09 0.12 0.14 0.09 CO [g/kWh] 1.87 2.42 2.53 2.72 Particle 2.07E+07 3.07E+06 1.43E+06 0.12E+06 number/cm3 CO2 [kg/kWh] 0.77 0.73 0.70 0.79

Example 2 Alcohol as Improver for Non-Diesel Fuel Upgrade

Three non-Diesel fuels, namely ethanol, n-butanol and gasoline were tested in the operation of a Diesel engine. These fuels alone or any mixture of them do not burn in a conventional Diesel engine, unless complex additives are used.

Table 3 presents the fuel mixtures considered in this example with conventional Diesel as a reference and six other fuel mixtures. Before upgrade according to the invention, none of these mixtures could power a Diesel engine. The non-Diesel fuels were upgraded by addition of alcohol and on-board catalytic dehydration prior to injection in the engine. The process conditions of dehydration reaction are chosen to provide a 80 or 85% conversion rate of alcohol to corresponding ether. This step upgrades the non-Diesel fuels into ether containing mixtures with Diesel-like ignition properties.

Table 3 shows that the upgraded fuels contain remaining alcohol and water together with ether.

TABLE 3 Fuel compositions - before and after upgrade Fuels Diesel E95 E85 E75 E60 B95 B85 Composition (weight %) before upgrade Ethanol — 95 85 75 60 — — n-Butanol — — — — — 95 85 Water —  5 — — —  5 — Gasoline — — 15 25 40 — 15 Diesel 100 — — — — — — Composition (weight %) after upgrade Ethanol — 14 17 15 12 — — DEE — 64 54 48 38 — — Water — 21 13 12  9 10  8 Butanol — — — — — 20 17 DBE — — — — — 70 60 gasoline — — 15 25 40 — 15 Diesel 100 — — — — — — Conversion alcohol to ether % 85 80 80 80 80 80

The upgraded fuels were used to operate a commercial Diesel engine R4 Peugeot 1.6 liter common rail engine (DV6TED4-9 HZ) of power 80 kW @4000 rpm. As these upgraded fuels differ from conventional Diesel fuel (lower heating value per volume), the engines settings were adapted for each case.

The engines settings were adapted for each case. For instance the fuel injection time was extended and started earlier in order to keep the pressure maximum in the range 8-12 degrees ATDC (standard Diesel operation). Table 4 and 5 summarizes the results for two different load points.

The fuel efficiency for the different fuels is in the same range and increases with the load. At low load (20 Nm), all fuels (conventional Diesel as well as the upgraded fuels) present an efficiency around 23-24% which is well in line with conventional Diesel operation. The non-Diesel fuels would not run the engine before upgrade, i.e. catalytic dehydration treatment, but after upgrade these fuels operate as Diesel-like fuels. The upgraded fuels are comparable in performance with conventional Diesel fuel. At higher load (55 Nm), this conclusion is still valid and the upgraded fuels perform very much like conventional Diesel fuel.

A considerable difference is seen when comparing the particle emissions. Indeed operation on the upgraded fuels E95 and E85 emits 30 to 40 times less particle than the reference fossil Diesel fuel.

The upgraded fuels enable to operate a Diesel engine with high efficiency, to reduce slightly the NOx emissions and to reduce particle emissions considerably when compared to conventional fossil Diesel fuel.

TABLE 4 Operation in a Diesel engine with load at 20 Nm Fuel Diesel E95 E85 E75 E60 B95 B85 Efficiency % 23.80 23.77 23.32 25.04 24.58 22.97 23.21 NOx 13.32 2.79 2.70 3.14 4.05 10.58 9.64 [g/kWh] HC^(§) 0.13 1.42 4.50 5.06 3.12 0.41 0.25 [g/kWh] CO [g/kWh] 9.27 55.41 58.10 51.26 52.81 8.43 10.81 ^(§)Hydrocarbons

TABLE 5 Operation in a Diesel engine with load at 55 Nm Fuel Diesel E95 E85 E75 E60 B95* B85 Effi- 34.74 31.65 33.91 34.32 34.07 36.12 33.17 ciency % NOx 10.17 6.59 5.95 7.73 7.72 12.02 9.84 [g/kWh] HC 0.09 0.16 0.17 0.20 0.22 0.11 0.06 [g/kWh] CO 1.87 4.93 8.14 10.01 11.93 0.98 1.73 [g/kWh] Particle 2.07E+6 0.07E+6 0.05E+6 — — — — number/ cm3 

1. Method for the preparation of a compression ignition engine fuel, comprising the steps of providing a mixture of a primary hydrocarbon fuel comprising one or more alcohols; and dehydrating in the mixture the one or more alcohol to its or their corresponding ether and water, to obtain the compression ignition fuel.
 2. The method of claim 1, wherein the primary hydrocarbon fuel contains C5-C28 hydrocarbons and/or bio-fuel.
 3. The method of claim 1, wherein the primary hydrocarbon fuel comprises gasoline.
 4. The method according to claim 1, wherein the one or more alcohols comprise C1 to C10 mono-alcohols and/or polyols.
 5. The method according to claim 1, wherein the one or more alcohols are normal C1 to C4 mono-alcohols.
 6. The method according to claim 1, wherein the one or more alcohols are dehydrated in presence of a dehydration catalyst.
 7. The method of claim 5, wherein the dehydration catalyst is arranged within a reactor on board of a vehicle.
 8. The method of claim 1, wherein the one or more alcohols contain up to 20 weight % of water. 